This invention relates generally to the art of manufacturing ribbon cartridges for printers used with equipment such as computers and word processors. More particularly, the present invention provides a method and apparatus for efficiently and accurately adjoining the ends of a length of ribbon so as to form a continuous ribbon loop extending through a ribbon cartridge. Still more particularly, the present invention relates to a printer ribbon welding system that joins two ribbon ends by means of an improved overlap welding and cutting method and apparatus, using either of two different cutting systems.
Continuous loop printer ribbon cartridges are in very common use throughout the world. In simple terms, they comprise a length of nylon or other fabric ribbon stuffed in serpentine fashion within a cartridge envelope and adjoined at the two ends to form a continuous loop. The weakest point along the ribbon loop, and thus the point that typically breaks soonest, is the fusion weld that joins the two ribbon ends. Thus, efforts to improve the durability of continuous loop ribbon cartridges frequently focus on improvements to the method and apparatus for forming the weld.
U.S. Pat. Nos. 4,629,530 and 4,935,081, which are expressly incorporated herein by reference, describe what is presently the most commonly used method and apparatus for joining two ribbon ends to form a continuous loop. The method and apparatus described in these patents is a substantial improvement over the "crash welding" technique previously in common use. Crash welding involves a simultaneous welding and cutting operation which imparts an excessive amount of energy into the fabric ribbon, weakening the ribbon and shortening the expected life of the cartridge.
In the improved technique described in U.S. Pat. Nos. 4,629,530 and 4,935,081, an operator clamps the two ribbon ends in criss-cross or x-pattern configuration across the top of an anvil having a narrow upper land surface (see FIG. 1 of U.S. Pat. No. 4,629,530). An ultrasonic horn moves into position above the crossed ribbon ends and the anvil and, without crushing the ribbon ends against the anvil, imparts ultrasonic energy into the ribbon ends, fusing the ribbon ends along a line defined by the adjacent land surface of the anvil.
Next, a separate cutter mechanism severs the two ends of the fused ribbon along the edge of the weld line or bead (see FIG. 2 of U.S. Pat. No. 4,629,530), and a mechanism rotates the upper ribbon 180.degree. to give a continuous length of ribbon joined along a diagonal weld bead (see FIG. 3 of U.S. Pat. No. 4,629,530). The weld formed by this technique leaves a distinct nub (see FIG. 4A of U.S. Pat. 4,629,530) that is unacceptable in terms of ribbon cartridge performance. Consequently, this technique typically also includes a second welding operation whereby the weld bead on the unfolded ribbon ends is reheated and flattened to reduce the nub to acceptable dimensions.
A different technique for joining two ribbon ends involves overlapping the two ribbon ends, rather than placing them in an x-pattern configuration, and forming a weld in the overlapped ribbon ends. This technique has an advantage over the technique described in U.S. Pat. Nos. 4,629,530 and 4,935,081 (the "x-pattern technique") in that a properly formed overlap weld can be stronger than a properly formed weld in criss-crossed ribbon ends. The overlap weld technique has a disadvantage, however, in that the problem of trimming the waste ribbon ends is substantially more difficult than in the x-pattern technique.
The x-pattern technique requires only a single, precise cut along one edge of the weld bead to sever the waste ribbon ends; whereas, the overlap technique requires two precise cuts on opposing faces of the ribbon to sever the waste ends. In addition, because the two cuts in overlapped ribbon ends must be made substantially in the plane of the ribbon and not in a perpendicular plane, as in the case of the x-pattern technique, the two cuts in overlapped ribbon ends are substantially more difficult to accomplish than the single cut in criss-crossed ribbon ends.
As a result of the difficulty in accomplishing the cutting operation in the overlap technique, it has never been widely used in the manufacture of continuous loop printer ribbon cartridges. Occasionally, some limited manufacturers have used the overlap technique and cut the waste ribbon ends by hand. This method, however, is very labor intensive, and thus expensive, and the quality of the result is variable at best. At least one manufacturer has developed an apparatus for making an overlap weld and automatically cutting the waste ribbon ends, but the quality of the result is not satisfactory.
Japanese Pat. Application Disclosure Kokai 63-132031, published Jun. 4, 1988, discloses the contents of Japanese Pat. Application No. 61-279209, filed Nov. 21, 1986 by Seidenshadenshi Kogyo Co., Ltd. for "A Device for Fusing and Straightening Fused Ends of a Ribbon." The disclosure describes an apparatus for forming an overlap weld in a continuous loop fabric ribbon. According to the disclosure, overlapped ribbon ends are clamped across the top of a support member (anvil), beneath an ultrasonic horn, with forked projections from a guide plate straddling the support member and positioned between the overlapped ribbon ends. The ultrasonic horn then moves down against the overlapped ribbon ends, fusing the ribbon along a line perpendicular to the longitudinal axis of the ribbon.
Next, the two clamps holding the fused ribbon ends simultaneously move along a pair of guide rails toward the guide plate. As the overlapped ribbon ends move toward the stationary guide plate, the forked projections from the guide plate converge around the weld bead between the two ribbon ends, wedging the waste ends up and down, respectively, away from the continuous ribbon loop. A pair of lasers, positioned above and below the guide plate in position to project laser beams at the waste ribbon ends along a line adjacent to the weld bead, then cut the waste ends from the ribbon loop.
Although the Seidenshadenshi apparatus represents an effort to construct a practical overlap welding system, it has problems. Most notably, heat is not a suitable manner by which to sever the waste ribbon ends, whether the heat is generated by a hot wire or by a laser. Heat causes the nylon fabric to form into beads along the severed edges. The beads of material are not dispersed during a second welding operation and tend to form hardened areas adjacent to the weld bead. These hardened areas inhibit the ability of the material to retain ink and to reproduce characters when struck by a printer and sometimes distort or break the wire shafts in a dot matrix printer. In addition, the heat generated by the laser beam, which must be projected very close to the weld bead in order to be effective, tends to overheat the nylon fabric within the adjacent weld bead, unnecessarily weakening the material.
Thus, it is apparent that a practical overlap welding system must include means for cutting the two waste ribbon ends by means of cutting blades. It would be advantageous to develop a method and apparatus for an overlap welding system that employs a mechanical cutting technique to sever the waste ribbon ends from the welded ribbon loop.